The Democratic Party debates among presidential candidates  expected to start in May or June of 2015  pose a serious threat to Hillary Clinton's candidacy. Her ability to suck up all the oxygen in the party's universe so far has succeeded in denying all but the most perfunctory coverage to her opponents. But the debates will change all that.

Democrats who oppose deeper involvement in Iraq or who scorn the crony capitalism of the Wall Street-Treasury Department-Federal Reserve-White House relationship will find their views echoed by the likes of former Virginia Sen. Jim Webb; Sen. Bernie Sanders, a Vermont independent; and Gov. Martin O'Malley of Maryland. These leftist alternatives to Clinton will gain traction, when the average Democrat gets to see and hear them in the presidential debates.

David Axelrod, who served as chief adviser to President Obama, made the astute observation that the sense of inevitability surrounding the former secretary of State's bid for the 2016 nomination has outstripped the rationale for her candidacy. But the hardest thing will be to convince the media to open its mind once it has slammed shut around the idea that Clinton will win the nomination. Based on public opinion polls, this conclusion stems from the fact that nobody knows much about her opponents  nor has Clinton had to defend her positions against them in the cut and thrust of debates.

There is a great temptation to see 2016 as a repetition of sorts of 1968. As Lyndon Baines Johnson (read: Clinton) moved to "inevitably" to take the nomination, the leading candidate who could stop him, Robert F. Kennedy (read: Elizabeth Warren), would not run. Into the breech stepped an unknown senator, Eugene McCarthy of Minnesota (read: Webb).

McCarthy had to wait for actual ballots to be cast in the first presidential primary, in New Hampshire, to show his political strength and Johnson's vulnerability. But Webb won't have to wait that long. It is easy to see how the former Virginia senator (or one of the other two challengers) could enter the debates with Clinton down by something on the order of 60 percent to 10 percent and emerge with big gains.

Such a turnaround would be heralded by the sensationalist media as an upset. The winner of the debate would suddenly be on the map, get money and attract media attention.

And, the sense of inevitability of Clinton's nomination would be shattered.

Even if Clinton parries attacks over her campaign donations (crony capitalism) and her backing of the War in Iraq (circa 2002), the very fact that the issues are raised will divide her vote. The left will rethink its blind commitment to her candidacy and challengers will have new appeal.

Clinton cannot cancel or opt not to attend the debates. Were she to fail to show, the failure would cost her much more than any performance in the debate might. Voters expect candidates to debate and will not tolerate those who refuse to appear.

Until Clinton's seemingly insurmountable lead has weathered the debates, she cannot be considered inevitable. As the sentiment against the Iraq War and Wall Street grows, the left will expand and disaffection with Clinton will increase.

Will this all attract Warren into the race as Kennedy was energized in 1968? Or will she stay out and leave the battle to one of the current alternatives? Either way, Clinton is not a done deal.